Bug 20376: Make select/unselect all ignore disabled checkboxes on batch record deletion

Bug 20376: Make select/unselect all ignore disabled checkboxes on batch record deletion

Test Plan:

0.1 - find at least one biblionumber that has at least one item checked out
0.2 - find at least one biblionumber that has zero items checked out.
1 - Go into the module "Tools > Batch record deletion"
2 - in "List of biblionumbers or authority ids (one per line)" put the values you found in step 0.1 and 0.2
3 - click continue
4 - biblionumbers with at least one item checked out should not be clickable.
5 - biblionumbers with zero items checked out should be clickable.
6 - click "Select all" and "Clear all", both buttons should change the "checked" status of the enabled AND disabled biblionumber checkboxes.
7 - apply patch
8 - click "Select all" and "Clear all", both buttons should change the "checked" status of ONLY the enabled biblionumber checkboxes.

Signed-off-by: JM Broust <jean-manuel.broust@univ-lyon2.fr>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>